This invention relates to an improved steering assembly for a road vehicle such as a passenger car. It in particular relates to a steering assembly of the electric power assisted steering (EPAS) type.
EPAS assemblies include an electric motor, which acts through a gearbox and optionally a clutch to apply an assistance torque to a steering shaft of a vehicle. The driver turns the steering shaft by applying a torque to a steering wheel, which is transferred to the steering shaft. The assistance torque applied by the motor acts to help the driver to turn the steering wheel, reducing the effort required for steering the vehicle.
The steering shaft and the motor need accurately to be held in a fixed position relative to one another during normal operation of the vehicle. However, in the event of an accident involving a rapid deceleration of the vehicle it is desirable for the steering assembly to collapse allowing the steering wheel to move towards the front of the vehicle under the weight of the driver. This has in the past been achieved in many ways. In one arrangement the steering shaft is manufactured as a single component with weakenings along its length permitting it to collapse axially by a controlled deformation as a force is applied to the steering wheel. In an alternative, it is known to provide a two-part steering shaft in which one part slides axially over the other as a force is applied to the steering wheel.
As well as allowing the steering shaft to collapse it is essential to permit the shroud, which encloses and supports the shaft to collapse. An example of such an arrangement is taught in our earlier application No. GB 9716747.2 In the assembly described in that application the shroud is provided in two sections with one section sliding into the other. To locate the steering shaft the lower section (furthest from the steering wheel) has two annular bearings, which support the steering shaft at spaced locations.
In some applications, typically on higher specification vehicles, it is also desirable for the steering wheel to be adjustable both for rake and for reach. Reach adjustment requires axial movement of the steering wheel away from or towards the driver. Such a range of adjustment permits the driver to obtain a more comfortable driving position. This further complicates the design of the steering assembly.
In many cases there is often a very limited space within which the collapsible assembly can be located. At least part of this space may be taken up by the electric motor and its housing making the provision of adequate crash protection a more demanding challenge than on a more traditional non-assisted steering system.
A collapsible assembly is known from EP0836981. and corresponding U.S. Pat. No. 5,988,679 which is incorporated by reference herein, in which both rake and reach adjustment can be made from a single lever. In use, a set of teeth on the end of a connecting pin are urged by the lever into engagement with a corresponding set of teeth formed on a shroud of a steering column. In the event of a crash the pin is intended to shear at a weakened section allowing the assembly to collapse. This has the disadvantage that a new pin is required after a collision and the shearing of the pin makes it inherently weak.